Java EE WEB工程师培训-JDBC+Servlet+JSP整合开发之14.Servlet请求头信息

2021-10-09 02:40:07

–典型的请求头信息
–读取HTTP请求头
–使用表格显示所有请求头信息
–理解各种请求头的含义
–区分不同的浏览器类型

##############Michael分割线###################

• 典型的请求头信息

Java EE WEB工程师培训-JDBC+Servlet+JSP整合开发之14.Servlet请求头信息

• 读取HTTP请求头
–使用HttpServletRequest中的方法
• 一般方法
–getHeader (header名称不区分大小写)
–getHeaders
–getHeaderNames
• 专门方法
–getCookies
–getAuthType
–getRemoteUser
–getContentLength
–getContentType
–getDateHeader
–getIntHeader
• 相关信息
–getMethod
–getRequestURI
–getQueryString
–getProtocol

• 使用表格显示有请求头信息

login.html

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
    <head>
        <title>login.html</title>
        <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
        <meta http-equiv="description" content="this is my page">
        <meta http-equiv="content-type" content="text/html; charset=UTF-8">
        

    </head>
    <body>
        <form name="f1" id="f1" action="/Servlet_RequestHeader/servlet/RequestHeaderServlet" method="post">
            <table border="0">
                <tr>
                    <td>Login:</td>
                    <td><input type="text" name="login" id="login"></td>
                </tr>
                <tr>
                    <td>Password:</td>
                    <td><input type="password" name="password" id="password"></td>
                </tr>
                <tr>
                    <td colspan="2" align="center"><input type="submit" value="login"></td>
                </tr>
            </table>
        </form>
    </body>
</html>

RequestHeaderServlet.java

package com.michael.servlet;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class RequestHeaderServlet extends HttpServlet {

        /**
         * Constructor of the object.
         */
        public RequestHeaderServlet() {
                super();
        }

        /**
         * Destruction of the servlet. <br>
         */
        public void destroy() {
                super.destroy(); // Just puts "destroy" string in log
                // Put your code here
        }

        /**
         * The doGet method of the servlet. <br>
         *
         * This method is called when a form has its tag value method equals to get.
         *
         * @param request the request send by the client to the server
         * @param response the response send by the server to the client
         * @throws ServletException if an error occurred
         * @throws IOException if an error occurred
         */
        public void doGet(HttpServletRequest request, HttpServletResponse response)
                        throws ServletException, IOException {

                doPost(request,response);
        }

        /**
         * The doPost method of the servlet. <br>
         *
         * This method is called when a form has its tag value method equals to post.
         *
         * @param request the request send by the client to the server
         * @param response the response send by the server to the client
         * @throws ServletException if an error occurred
         * @throws IOException if an error occurred
         */
        public void doPost(HttpServletRequest request, HttpServletResponse response)
                        throws ServletException, IOException {
                Enumeration names = request.getHeaderNames();

                response.setContentType("text/html");
                PrintWriter out = response.getWriter();
                out
                                .println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
                out.println("<HTML>");
                out.println("    <HEAD><TITLE>A Servlet</TITLE></HEAD>");
                out.println("    <BODY>");

                out.println("<table>");
                out.println("<tr>");
                out.println("<th>");
                out.println("RequestHeader Name");
                out.println("</th>");
                out.println("<th>");
                out.println("RequestHeader Value");
                out.println("</th>");
                out.println("</tr>");
                while(names.hasMoreElements()){
                        String name = (String) names.nextElement();
                        String value = request.getHeader(name);
                        out.println("<tr>");
                        out.println("<td>");
                        out.println(name);
                        out.println("</td>");
                        out.println("<td>");
                        out.println(value);
                        out.println("</td>");
                        out.println("</tr>");
                }
                out.println("</table>");
                out.println("    </BODY>");
                out.println("</HTML>");
                out.flush();
                out.close();
        }

        /**
         * Initialization of the servlet. <br>
         *
         * @throws ServletException if an error occure
         */
        public void init() throws ServletException {
                // Put your code here
        }

}

看下效果

• 理解各种请求头的含义
– Accept
• 标识浏览器能处理MIME类型
• 能发送不同的内容到不同的客户端. 例如，PNG文件有好的压缩特性，但是在浏览器中支持的不是很广泛。
• 一个Servlet可以检查是否支持PNG文件格式，如果支持
– <IMG SRC=“picture.png” ...> 否则
– <IMG SRC="picture.gif" ...>
– Accept-Encoding
• 标识浏览器能处理的编码类型
– Authorization
• 授权信息，通常出现在对服务器发送的WWW-Authenticate头的应答中
– Connection
• 表示是否需要持久连接。如果Servlet看到这里的值为“Keep-Alive”，或者看到请求使用的是HTTP 1.1（HTTP 1.1默认进行持久连接），它就可以利用持久连接的优点，当页面包含多个元素时（例如Applet，图片），显著地减少下载所需要的时间。要实现这一点，Servlet需要在应答中发送一个Content-Length头，最简单的实现方法是：先把内容写入ByteArrayOutputStream，然后在正式写出内容之前计算它的大小。
– Cookie
• 参考Java EE WEB工程师培训-JDBC+Servlet+JSP整合开发之16.Cookie

–Host
• 包含一个URL，用户从该URL代表的页面出发访问当前请求的页面
–If-Modified-Since
• 只有当所请求的内容，在指定的日期之后，又经过修改才返回它，否则返回304“Not Modified”应答
–Referer
• 包含一个URL，用户从该URL代表的页面出发访问当前请求的页面。
–User-Agent
• 浏览器类型，如果Servlet返回的内容与浏览器类型有关则该值非常有用。

• 区分不同的浏览器类型

BrowserTypeServlet.java

package com.michael.servlet;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class BrowserTypeServlet extends HttpServlet {

        /**
         * Constructor of the object.
         */
        public BrowserTypeServlet() {
                super();
        }

        /**
         * Destruction of the servlet. <br>
         */
        public void destroy() {
                super.destroy(); // Just puts "destroy" string in log
                // Put your code here
        }

        /**
         * The doGet method of the servlet. <br>
         *
         * This method is called when a form has its tag value method equals to get.
         *
         * @param request the request send by the client to the server
         * @param response the response send by the server to the client
         * @throws ServletException if an error occurred
         * @throws IOException if an error occurred
         */
        public void doGet(HttpServletRequest request, HttpServletResponse response)
                        throws ServletException, IOException {

                doPost(request,response);
        }

        /**
         * The doPost method of the servlet. <br>
         *
         * This method is called when a form has its tag value method equals to post.
         *
         * @param request the request send by the client to the server
         * @param response the response send by the server to the client
         * @throws ServletException if an error occurred
         * @throws IOException if an error occurred
         */
        public void doPost(HttpServletRequest request, HttpServletResponse response)
                        throws ServletException, IOException {
                String browserName = request.getHeader("user-agent");
                String result="";
                if(browserName.indexOf("MSIE")!=-1){
                        result = "您当前使用的浏览器是IE!";
                }else{
                        result = "您当前使用的浏览器是FireFox!";
                }

                response.setContentType("text/html;charset=gbk");
                PrintWriter out = response.getWriter();
                out
                                .println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
                out.println("<HTML>");
                out.println("    <HEAD><TITLE>A Servlet</TITLE></HEAD>");
                out.println("    <BODY>");
                out.println(result);
                out.println("    </BODY>");
                out.println("</HTML>");
                out.flush();
                out.close();
        }

        /**
         * Initialization of the servlet. <br>
         *
         * @throws ServletException if an error occure
         */
        public void init() throws ServletException {
                // Put your code here
        }

}

测试

OK!

##############Michael分割线###################

附件：http://down.51cto.com/data/2353111

本文转自redking51CTO博客，原文链接：http://blog.51cto.com/redking/168678，如需转载请自行联系原作者

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